Actinic keratosis (AKs) is a precancerous (premalignant) skin disorder caused by or associated with chronic exposure to radiant energy, such as sunlight. Actinic keratosis lesions are small, red, rough spots or lesions occurring on sun exposed areas of the skin. Actinic keratosis lesions possess many of the same cellular changes observed in a skin cancer called squamous cell carcinoma (SCC). Research shows that a mutated version of the p53 gene is found in sun-damaged cells in the body and is present in more than about 90% of people who have AKs and squamous cell carcinomas. Although most actinic keratosis lesions do not actually become cancerous, some lesions can become malignant.
It is believed that actinic keratosis develops in skin cells called “keratinocytes”, which are the cells that constitute about 90% of the epidermis, the outermost layer of skin. Chronic sun exposure, over time, generates mutations in these cells and causes the cells to change in size, shape, the way they are organized, and the way they behave. In addition, the cellular damage can even extend to the dermis, the layer of skin beneath the epidermis.
Actinic keratosis lesions generally measure in size between about 2 to about 6 millimeters in diameter, AK lesions can range in color from skin-toned to reddish and often have a white scale on top. On occasion, AK lesions will form into the shape of animal horns. When this occurs, the AKs are known as “cutaneous horns.”
People who are at higher risk for developing actinic keratosis tend to be fair-skinned and spend significant time outdoors, e.g., at work or at play, over the course of many years. AK lesions usually develop on those areas of the body that have been constantly exposed to the sun for years. Additionally, the skin often becomes wrinkled, mottled, and discolored from chronic sun exposure. Common locations for actinic keratosis include the face, ears, lips, balding scalp, back of the neck, upper chest, the tops of the hands and forearms. When AK lesions develop on the lips, the condition is known as actinic cheilitis. Actinic cheilitis can be characterized by a diffuse scaling on the lower lip that cracks and dries. In some cases, the lips will have a whitish discoloration on the thickened lip.
Actinic keratosis is generally more common after age 40, because actinic keratosis take years to develop. However, even younger adults may develop actinic keratosis when living in geographic areas that are exposed to high-intensity sunlight year round, such as Florida and Southern California.
Actinic keratosis has become a significant health care issue in the United States of America. It is estimated that over 20 million Americans suffer from actinic keratosis, and that that number continues to grow. In fact, actinic keratosis is so common today that treatment for actinic keratosis ranks as one of the most frequent reasons people consult a dermatologist.
The compound characterized as 1-isobutyl-1H-imidazo[4,5-c]-quinolin-4-amine or 1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine, and known as imiquimod, is disclosed in U.S. Pat. No. 4,689,338 and described therein as an antiviral agent and as an interferon inducer, which is incorporated herein by reference in its entirety. A variety of formulations for topical administration of imiquimod are also described therein. This U.S. Pat. No. 4,689,338 is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,751,087 discloses the use of a combination of ethyl oleate and glyceryl monolaurate as a skin penetration enhancer for nitroglycerin, with all three components being contained in the adhesive layer of a transdermal patch, wherein this U.S. patent is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,411,893 discloses the use of N,N-dimethyldodecylamine-N-oxide as a skin penetration enhancer in aqueous systems, wherein this U.S. patent is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,722,941 discloses readily absorbable pharmaceutical compositions that comprise a pharmacologically active agent distributed in a vehicle comprising an absorption-enhancing amount of at least one fatty acid containing 6 to 12 carbon atoms and optionally a fatty acid monoglyceride. Such compositions are said to be particularly useful for increasing the absorption of pharmacologically active bases, wherein this U.S. patent is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,746,515 discloses a method of using glyceryl monolaurate to enhance the transdermal flux of a transdermally deliverable drug through intact skin, wherein this U.S. patent is incorporated herein by reference in its entirety.
U.S. Pat. Nos. 5,238,944, 7,038,051, 6,693,113, 6,894,060 U.S. Patent Publication No. 2007/0123558, U.S. Patent Publication No. 2004/087614, U.S. Patent Publication No. 2002/147210, and WO2008US53522 disclose topical formulations and/or topical and transdermal delivery systems containing 1-isobutyl-1H-imidazo[4,5-c]-quinolin-4-amine or 1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine, wherein each are incorporated herein by reference in their entireties.
Currently, the FDA has approved a 5% imiquimod cream, commercially available under the brand name Aldara®, to treat certain dermal and mucosal associated conditions, such as (1) the topical treatment of clinically typical, nonhyperkeratotic actinic keratosis (AK) on the face or scalp in immunocompetent adults, (2) topical treatment of biopsy-confirmed, primary superficial basal cell carcinoma (sBCC) in immunocompetent adults, and (3) the topical treatment of external genital and perianal warts/condyloma acuminate in patients 12 years or older.
Aldara® is the brand name for an FDA-approved 5% imiquimod cream, which is an immune response modifier. Each gram of the Aldara® 5% imiquimod cream contains 50 mg of imiquimod in an off-white oil-in-water vanishing cream base consisting of isostearic acid, cetyl alcohol, stearyl alcohol, white petrolatum, polysorbate 60, sorbitan monostearate, glycerin, xanthan gum, purified water, benzyl alcohol, methylparaben, and propylparaben. The Aldara® 5% imiquimod cream is packaged in single-use packets or sachets, each containing 250 mg of cream, equivalent to 12.5 mg of imiquimod.
Chemically, imiquimod, as indicated above, is known as 1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine or 1-isobutyl-1H-imidazo[4,5-c]-quinolin-4-amine. Imiquimod has a molecular formula of C14H16N4 and a molecular weight of 240.3. The chemical structural formula for imiquimod is as follows:

Notwithstanding FDA approval, Aldara® 5% imiquimod cream treatment is not without limitation, including an unsimplified and lengthy dosing regimen. Generally speaking, the treatment regimen for actinic keratosis using FDA-approved Aldara® 5% imiquimod cream consists of applying the Aldara® 5% imiquimod cream two times per week for a full 16 weeks to a defined/limited treatment area on the face or scalp (but not both concurrently). The surface treatment area for Aldara® 5% imiquimod cream is limited to approximately 25 cm2 (e.g., a 5 cm×5 cm area, which may be of any shape; the treatment area does not have to be square) and is defined as one contiguous area. The number of AK lesions treated with Aldara® 5% imiquimod cream per treatment area is generally between about 4 and about 8. Because the treatment area is quite small, less than one single-use Aldara® packet or sachet (250 mg of total cream, of which 12.5 mg is imiquimod) is generally used per application. Inconsistencies in both compliance and therapeutic results frequently occur with the treatment of actinic keratosis with FDA-approved Aldara® 5% imiquimod cream due to the lengthy treatment period, i.e., 16 weeks, the complicated dosing regimen, i.e., twice weekly, and the high incidence of application site reactions.
Subsequent to FDA-approval of Aldara® 5% imiquimod cream to treat actinic keratosis, a pilot study was conducted that was an open-label trial that included 25 patients who had between 5 and 20 discrete AKs within a cosmetic unit of the forehead, scalp, or cheek. During this pilot study, treatment consisted of once-daily application of 5% imiquimod cream, three times a week for four weeks to the entire cosmetic unit, followed by a rest period of four weeks. The cycle was repeated if any AKs remained after a complete eight-week cycle. A maximum of three cycles was permitted (24 weeks). Thirty-three sites (i.e., cosmetic units) in 25 subjects were evaluated. According to the authors, compliance was excellent with a very tolerable safety profile. Complete clearing of all AKs was noted in 82% (27/33) of anatomic sites in 25 study subjects. Almost half the sites (15/33) were clear at the end of the first cycle. A “therapeutic interval” was noted during the rest period wherein clinical inflammation subsided but AKs continued to clear. An added effect, according to the authors, was the uncovering and clinical appearance and subsequent eradication of incipient (subclinical) AKs in the treatment area. As a result, the authors concluded that there was excellent compliance with the cycle therapy regimen utilized in this study and that the identification of a therapeutic interval may prove to be beneficial in formulating individualized dosing regimens. The authors warned, however, that the findings of the study must be evaluated cautiously. The authors also cautioned that, because this study was an open-label trial in a small number of study subjects, safety, efficacy and duration of efficacy needs to be corroborated by controlled, randomized trials with larger study populations. See Salasche S. J., Levine N., and Morrison L.: Cycle therapy of actinic keratoses of the face and scalp with 5% topical imiquimod cream: An open-label trial. J Am Acad Dermatol. 47(4):571-7 (October 2002).
Also subsequent to FDA-approval of Aldara® 5% imiquimod cream to treat actinic keratosis, a dual-center, randomized, double-blind, vehicle-controlled study was conducted to evaluate the safety and efficacy of short courses of therapy with Aldara® 5% imiquimod cream in clearing ≥75% of baseline solar keratoses (“SK”) within a field of treatment. Subjects with 5-15 baseline SK within one treatment area (scalp, forehead and temples, or both cheeks) were randomized to apply imiquimod or vehicle cream to the entire treatment area three times a week for 3 weeks. Subjects were assessed 4 weeks after completing the first course for clearance of lesions. Subjects with <75% clearance were commenced on a second 3-week course of study cream. Subjects with ≥75% clearance were followed up until study completion without further therapy. All subjects were evaluated at the study endpoint of 14 weeks after initiating therapy for assessment of the primary outcome (≥75% clearance of baseline solar keratoses). According to the authors, twenty-one out of 29 (72%) imiquimod-treated subjects cleared ≥75% of baseline lesions compared with 3/10 (30%) subjects using the vehicle cream (Fisher's exact test, P=0.027) and the imiquimod was well tolerated. Also according to the authors, the results of this study suggest that 5% imiquimod administered three times per week may offer a therapeutic alternative to patients with SK on the face, and scalp, and that one or two short courses may be an alternative to the continuous longer Aldara® 5% imiquimod cream therapy approved by the FDA. The authors did caution, however, that, because the study had a relatively short follow-up endpoint, additional studies may be needed to evaluate if the therapeutic outcome can be sustained. See Chen K. et al.: Links Short-course therapy with imiquimod 5% cream for solar keratoses: a randomized controlled trial. Australasian J Dermatol. 44(4):250-5 (November 2005).
In addition, a multi-center, vehicle-controlled, double-blind study to assess the safety and efficacy of imiquimod 5% cream applied once daily 3 days per week in one or two courses of treatment of actinic keratoses on the head was conducted and reported in 2007. According to the authors, a total of 259 patients diagnosed with AK were enrolled in twenty study centers in Europe and applied imiquimod for 4 weeks, entered a 4-week rest period and if they did not have complete clearance, the patients then entered a second course of treatment. The area of treatment was confined to about 25 cm2. As reported by the authors, patients in the imiquimod group had an overall complete clearance rate of 55.0% (71/129) vs. a rate of 2.3% (3/130) for the vehicle group and that there was a high rate of agreement between the clinical assessment and histological findings with respect to AK lesion clearance. The authors further reported that, at both 8-week post-treatment visits, the negative predictive value of the investigator assessment was 92.2% for clinical assessments vs. histological results. The authors concluded that a 4-week course of treatment with three times weekly dosing of imiquimod 5% cream, with a repeated course of treatment for those patients who fail to clear after the first course of treatment, is a safe and effective treatment for AK, and the overall complete clearance rate (complete clearance after either course 1 or course 2) is comparable to the 16-week Aldara® 5% imiquimod cream treatment regimen, while decreasing drug exposure to the patient and decreasing the overall treatment time. See Alomar, A., J. Bichel, et al.: Vehicle-controlled, randomized, double-blind study to assess safety and efficacy of imiquimod 5% cream applied once daily 3 days per week in one or two courses of treatment of actinic keratoses on the head. British Journal of Dermatology. 157(1): 133-41 (2007).
Another vehicle-controlled, double-blind, randomized study of imiquimod 5% cream applied 3 days per week in one or two courses of treatment for actinic keratoses on the head was conducted and also reported in 2007. According to the authors, patients with actinic keratosis lesions on the head applied imiquimod or vehicle cream 3×/wk for 4 weeks (course 1), patients with remaining lesions received another course of treatment, and complete and partial clearance rates were evaluated after course 1, after course 2 (overall), and 1 year later. The authors concluded that imiquimod 3×/wk in one or two courses of treatment appears to be effective for the treatment of actinic keratoses on the head, providing long-term clinical benefits and that some recurrences do occur, so long-term follow-up is recommended. See Jorizzo, J., S. Dinehart, et al.: Vehicle-controlled, double-blind, randomized study of imiquimod 5% cream applied 3 days per week in one or two courses of treatment for actinic keratoses on the head. Journal of the American Academy of Dermatology. 57(2): 265-8 (2007).
Another multicenter, open-label study using imiquimod 5% cream in one or two 4-week courses of treatment for multiple actinic keratoses on the head was conducted and also reported in 2007. According to the authors, this was an open-label, phase IIIb study involving 180 dermatology clinics and practices in Germany, and patients were eligible if they had clinically typical, visible AK lesions located anywhere on the head, excluding the upper and lower eyelids, nostrils, lip vermilion, and inside the ears. The authors reported that patients applied imiquimod study cream to the treatment area once daily 3×/week for 4 weeks (course 1) followed by a 4-week post treatment period and that patients with AK lesions remaining in the treatment area underwent a second 4-week treatment course. Apparently, the treatment area was not restricted and patients were allowed to use one or two sachets per application. The size of the treatment areas and number of sachets applied were not reported. The median number of AK lesions at baseline was 7. The authors further reported that 829 patients entered the study and that, overall, the complete clearance rate was 68.9% (571/829), the partial clearance rate (percentage of patients with ≥75% reduction in the number of baseline AK lesions) was 80.2%. The authors acknowledged that local skin reactions (LSRs) and application site reactions (ASRs) were the most commonly reported adverse events, and that four patients discontinued from the study due to LSRs or ASRs. The authors concluded that a shorter treatment regimen of imiquimod 5% cream, i.e., once daily 3×/week for 4 weeks for 1 or two courses, can produce complete clearance rates similar to those seen with 16 weeks of Aldara® 5% imiquimod cream treatment and has the advantage of lower drug exposure, resulting in a better benefit-risk profile for the patient. See Stockfleth, E., W. Sterry, et al.: Multicentre, open-label study using imiquimod 5% cream in one or two 4-week courses of treatment for multiple actinic keratoses on the head. British Journal of Dermatology. 157 Suppl 2: 41-6 (2007).
Another randomized study of topical 5% imiquimod vs. topical 5-fluorouracil vs. cryosurgery in immunocompetent patients with actinic keratoses, including a comparison of clinical and histological outcomes including 1-year follow-up, was conducted. According to the authors, this study compared the initial and 12-month clinical clearance, histological clearance, and cosmetic outcomes of topically applied 5% imiquimod (IMIQ) cream, 5% 5-fluorouracil (5-FU) ointment and cryosurgery for the treatment of AK of patients who were randomized to one of the following three treatment groups: one or two courses of cryosurgery (20-40 seconds per lesion), topical 5-FU (twice daily for 4 weeks), or one or two courses of topical imiquimod (three times per week for 4 weeks each). In this study, the treatment area was confined to one anatomic area of 50 cm2 or less. The authors reported that: (1) sixty-eight percent (17/25) of patients treated with cryosurgery, 96% (23/24) of patients treated with 5-FU, and 85% (22/26) of patients treated with IMIQ achieved initial clinical clearance, P=0.03; (2) the histological clearance rate for cryosurgery was 32% (8/25), 67% (16/24) for 5-FU, and 73% (19/26) in the imiquimod group, P=0.03; (3) the 12-month follow-up showed a high rate of recurrent and new lesions in the 5-FU and cryosurgery arms; (4) the sustained clearance rate of initially cleared individual lesions was 28% (7/25) for cryosurgery, 54% (13/24) for 5-FU and 73% (19/26) for imiquimod (p<0.01); (5) sustained clearance of the total treatment field was 4% (1/25), 33% (8/24), and 73% (19/26) of patients after cryosurgery, 5-FU, and imiquimod, respectively (P<0.01); and (6) the patients in the imiquimod group were judged to have the best cosmetic outcomes (P=0.0001). The authors concluded that imiquimod treatment of AK resulted in superior sustained clearance and cosmetic outcomes compared with cryosurgery and 5-FU and that imiquimod should be considered as a first line therapy for sustained treatment of AK. See Krawtchenko, N., J. Roewert-Huber, et al.: A randomized study of topical 5% imiquimod vs. topical 5-fluorouracil vs. cryosurgery in immunocompetent patients with actinic keratoses: a comparison of clinical and histological outcomes including 1-year follow-up. British Journal of Dermatology. 157 Suppl 2: 34-40 (2007).
Also subsequent to FDA-approval of Aldara® 5% imiquimod cream to treat actinic keratosis, an open-label study to assess the safety and efficacy of imiquimod 5% cream applied once daily three times per week in cycles for treatment of actinic keratoses on the head was conducted. During this open-label study, imiquimod 5% cream was administered three times per week for four weeks followed by four weeks of rest (cycle 1) to AK lesions on the head. If AK lesions remained visible at the end of cycle 1, a second treatment cycle was instituted. According to the authors, 50% (30 of 60) of the subjects who experienced complete clearance of AK lesions, and 75% (30 of 40) of the subjects who experienced partial clearance of AK lesions after imiquimod treatment at the end of cycle 2. The authors further reported that 77% of the subjects, who achieved complete clearance, had no visible AK lesions 12 weeks post-treatment and that the imiquimod was well tolerated. The authors concluded that 5% Imiquimod cycle therapy, when administered three time per week for four weeks followed by four weeks of rest (cycle 1) combined with a second treatment cycle repeat, may be a safe and effective alternative to continuous imiquimod therapy for the treatment of AK lesions. The authors cautioned, however, that while cycle therapy does not affect the short-term AK recurrence rate, long-term follow-up is required. The authors also cautioned that further randomized, vehicle-controlled trials are needed. See Rivers J. K. et al.: Open-label study to assess the safety and efficacy of imiquimod 5% cream applied once daily three times per week in cycles for treatment of actinic keratoses on the head. J Cutan Med Surg. 12(3):97-101 (May-June 2008).
In view of the above, there is a need for improved actinic keratosis topical treatment that overcomes the current limitations associated with the current FDA-approved topical treatment regimen for actinic keratosis, i.e., 16 weeks, twice per week, with FDA-approved Aldara® 5% imiquimod cream.